Lessons learned from dog days of summer

Holstein dairy cows.

Last week was a miserable one for many of us with hay that would not dry and cows and calves under heat stress, but there were lessons to be learned. 

The first is that you will spend even more time than normal sitting at the computer. Utilizing activity data and rumination data to manage cows has become an important part of cow management on our farm. The activity data has been a great addition for heat and illness detection. 

The challenge starts when the environment’s heat loads surpassed our barn’s ability to keep the cows cool. The low activity alerts and decreased rumination will make your head spin, as you try to determine if anyone is actually sick or just hot. 

There are two lessons here, one being that you should focus on evening activity — although with nighttime temperatures staying above 70 degrees Fahrenheit, evening heat dissipation and return to normal activity was decreased. It still helped to determine who was extra lethargic. 

The other lesson is that a deep dive into a cow’s production data to determine who has better genetics to manage heat stress can have long-term benefits. While this may not be a primary decision for culling or keeping a cow or her offspring, it is something to enter in the cow’s records. 

If weather patterns continue to swing with more hot days than cold days, this information could help you select the high-profit cows that also handle heat better for future herd genetic improvement. 

The next lesson learned was to start making a winter projects list of barn improvements to better manage these conditions. 

Monitoring vital statistics

My list had two barns on it where the cows or heifers were not handling the heat as well. These issues were identified by watching the animal’s respiration rates, body temperature and physical appearance.

Respiration rates are the recommended measure of heat stress because there is little to no lag time compared to body temperatures and milk production. Normal respiratory rates for adult dairy cattle range from 40 to 60 breaths per minute (bpm). 

If more than 10% of cows have a respiratory rate exceeding 100 bpm, the situation is considered an emergency, and immediate action should be taken. Body temperature gives a direct measure of an individual cow’s heat stress level. 

Normal body temperature for an adult cow is 101.5 to 102.5 degrees Fahrenheit. If more than 5-10% of cows have a body temperature above 105 degrees Fahrenheit, the situation is considered an emergency and immediate action should be taken. 

Physical appearance is the least useful in adult cows but very helpful in young calves. Cows experiencing mild heat stress may not show clinical signs at all. Cows experiencing severe heat stress usually breathe with their mouths open and pant with their necks extended. They are lethargic and may appear unsteady. 

When calves are experiencing heat stress, they often appear lethargic and have decreased appetites. 

Barn fixes

My simplest fix was in a heifer barn where only one heifer who had been identified as having chronic lung issues due to pneumonia was showing severe heat stress. This barn has high block walls and already had all siding removed and a fan in the worst area. 

The issue in this barn is that no air can exhaust through the barn ridge. One morning, the barn was so hot and humid it was dripping. The solution could have been to have fewer animals in the barn, but we are choosing to open the ridge. 

A breeding age and older livestock barn ridge vent should be one foot wide for a 40-foot-wide barn with an additional three inches for every 10 feet of barn width over 40 feet. This ridge vent will improve both summer and winter air quality. 

The second issue was in the milk cow barn, where we had decreased feed intake on about 10% of the herd based on time eating. Checking fan placement showed the barn had good air movement of 5 mph even in the areas usually identified as dead zones. Soakers were also in use at the parlor exits and holding area. 

The issue was water space and volume available due to an increase in cow numbers. A minimum of 2 linear inches of drinking space per cow should be provided year around with more during hot weather and water capacity of 25-35 gallons per cow. 

These small fixes will improve our farm’s ability to manage heat stress in the future.


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